1. Field of the Invention
The present invention relates to a novel high purity 9,9-bis (4-hydroxyphenyl) fluorene and to methods of preparation and purification thereof.
2. Background of the Art
In the modern polymeric manufacturing industry, bisphenols are used on a large scale in polycondensation reactions, particularly as monomers in the preparation of epoxy resins, polyurethanes, polycarbonates, polyethers and polyesters with especially high thermal resistance and good optical properties.
The compound 9,9-Bis-(4-HydroxyPhenyl) Fluorene and its substituted derivatives, generically known as BHPF, or Bisphenol F, is a useful monomer for the synthesis of the above mentioned polymers, particularly for the synthesis of polyesters, and especially for the preparation of polyarylates, i.e., polymers obtained from the copolymerization of BHPF with diacylic halides. These diacylic halide compounds show very high thermal resistance and exceptional optical properties (xe2x80x9cHigh Performance Polyestersxe2x80x9d).
High performance polyesters, and particularly, aromatic polyesters, known as xe2x80x9cpolyarylatesxe2x80x9d, have several important applications, such as:
1. polymeric films with mechanical properties higher than typical for a class of polymers, to be used in mechanical components where the resistance to a high number of stress-strain cycles (e.g., automotive components) is required;
2. replacement of glass, using films with very good optical properties, with good transparency to all the visible wavelength, low Yellow Index (e.g., as a components in liquid crystalxe2x80x94displays, ophthalmic lenses, goggle lenses, etc.);
3. thin films (under 10 xcexcm) with good electrical insulation properties, especially at high temperatures (above 100xc2x0 C.), e.g., for use with high performance electrical capacitors;
4. films suitable for the deposition of metal layers (e.g., copper, for the production of printed flexible circuits) or transparent conductive layers (e.g., ITO, Indium Tin Oxide).
These applications require polymeric materials with a very high glass transition temperature (Tg), for example above 300xc2x0 C., a very high softening temperature and a very high melting temperature. A very high average molecular weight (AMW) (for example, above 500,000 Dalton), a narrow molecular weight distribution (MWD) and a low content of unreacted monomers or low molecular weight oligomers are other fundamental requirements desirable in high performance polyesters. These parameters are very important for the thermal and optical properties of these materials.
These results could be achieved previously only with the use of high purity reactants in the polymerization process, due to a well-known problem of polycondensation reactions (also known as a xe2x80x9cstep polymerizationxe2x80x9d). A description of this problem can be found in G. Odian, Principles of Polymerization, Chapter 2, xe2x80x9cStep Polymerizationxe2x80x9d, page 41, 3rd Ed., John Wiley and Sons, Inc. New York, 1991.
The successful synthesis of high molecular weight polycondensation polymers can be achieved only at very high conversion rates (generally higher than 99%, better higher than 99.5%), and this places several stringent requirements on the reaction conditions, such as a favorable equilibrium and the absence of side reactions.
This last requirement is strictly related to the above mentioned high purity of the reactants involved in the polymerization reaction, and the purity of the bisphenol(s) used in this reaction is one of the main issues in controlling the direction and existence of side reactions, because the presence, even in traces, of reactants or catalysts used in their synthesis, or the presence of reaction by-products can have a strong impact on the final result of the polymerization, often decreasing the molecular weight of the polymer. The separation of these by-products from the main product is of fondamental importance, because the different reactivities or functionalities of these by-products can have a heavy negative impact on the polymerization reactions, lowering the conversion degree of the reactants into the polymer and giving lower average molecular weight or introducing chain branching inside the structure of the final polymer. The separation process must be able to eliminate also the traces of reactants that can be present in the reaction product, because the most of them (phenols, acid catalysts) could react with e.g., the diacylic halides, breaking the polymerization reaction because of their monofunctionality or their different reactivity.
Several methods for the purification of BHPF are described in the art. The known methods are rather complex or involve large amounts of water or mixtures such as of water/organic solvents (e.g., alcohols, acetone or other carbonilic compounds), to eliminate from the product the residual catalysts (acids) or the excess of phenol used in the synthesis reaction. A great number of examples in literature also describe the use of halogenated solvents in the purification steps, such as methylene chloride, 1,2 dichloroethane, trichloroethylene and tetrachloroethane, which raise severe problems from the environmental and safety points of view.
U.S. Pat. No. 3,546,165 describes the synthesis of soluble, high melting, thermally stable linear polyesters. Example II describes the preparation of the 9,9-bis (4-hydroxyphenyl) fluorene by reaction of the reactants in molten phenol, precipitation with water and purification with toluene. The final product has a melting point of 224xc2x0 C.
U.S. Pat. No. 4,024,194 describes a method for the purification of BHPF where the by-products, identified as 9-(4-hydroxyphenyl)-9-(2-hydroxyphenyl) fluorene (ortho-, para-isomer of BHPF) are eliminated using nitromethane (CH3NO2) as a solvent of crystallization. The final product has a melting point range of 224.8-225.4xc2x0 C. and less than 0.5% of the aforesaid impurity.
U.S. Pat. No. 4,049,721 describes a method for purifying BHPF containing phenol as an impurity by using methanol and water and/or mixtures thereof.
U.S. Pat. Nos. 4,387,209, 4,401,803, 4,430,493, 4,446,195 and WO 92/03493 describe a process for the preparation of aromatic polyesters by using BHPF having a melting range of from 228xc2x0 to 230xc2x0 C. All patents make reference to U.S. Pat. No. 4,467,122 for the preparation of such BHPF by reaction of fluorenone in melted phenols in the presence of gaseous hydrogen halide and catalytic amounts of divalent, trivalent or tetravalent metal halides (where metal is selected from Ca, Fe, Ti, Sn and Al). The purification method includes washing with water and 1,2-dichloroethane to obtain a purity of 99.8% (determined by HPLC).
U.S. Pat. No. 4,675,458 describes a preparation method of BHPF by reacting fluorenone and phenol in presence of sulfuric acid having a concentration greater than 75% and mercaptans, as condensing agent. Methanol and isopropanol are used for purification, and the isolated product showed a melting point of 223xc2x0 C.
U.S. Pat. No. 4,931,594 describes the synthesis of BHPF by reacting phenol and fluorenone in presence of an insoluble, strong acidic ion cationic exchange resin as a condensation catalyst, in a range of temperature between 20xc2x0 C. to 150xc2x0 C. The product was washed with acetone, water and isopropanol to give a final product showing a melting point between 221xc2x0 C.-224xc2x0 C.
U.S. Pat. No. 5,110,994 describes a method for the preparation of BHPF where the fluorenone is reacted in presence of an excess of phenol, hydrochloric acid and aluminum trichloride as catalyst, and the catalyst is dissolved in an anhydrous organic solvent. The raw product is treated with boiling water, acetone, and 1,2-dichloroethane. The final product has a DSC onset melting temperature of 225.5xc2x0 C.
U.S. Pat. No. 5,149,886 describes a process for the synthesis of BHPF by condensing fluorenone and phenol in a molar ratio of 1:4 to 1:8 at 30 to 90xc2x0 C. in the presence of gaseous hydrogen chloride and xcex2-mercaptopropionic acid catalyst, where the improvement comprises distilling water of reaction and dissolved hydrochloridric acid from the complete reaction mixture, dissolving the distillation residue in a nitrile, separating the crystallized adduct of nitrile and BHPF from the nitrile and dissociating the adduct to recover BHPF. Acetonitrile, propionitrile, adipic acid dinitrile, fumaric acid dinitrile, glutaric acid dinitrile, and octanoic acid diitrile are disclosed as nitrites.
U.S. Pat. No. 5,169,990 discloses the synthesis of BHPF by condensation of fluorenone and phenol in a molar ratio of 1:4 to 1:8, in the presence of gaseous hydrogen chloride, and xcex2-mercaptopropionic acid as catalyst where the completed reaction mixture is mixed with a polyalkylene glycol and then the excess of phenol is distilled from the mixture. Purity of 99.8% by HLC method is obtained with recrystalization in toluene/isopropanol or acetonitrile.
U.S. Pat. No. 5,248,838 describes a method for the synthesis of BHPF where the reactants are dissolved in an organic solvent (hydrocarbon solvents) and the BHPF is not soluble in this solvent at room temperature.
U.S. Pat. No. 5,304,688 describes the synthesis of BHPF in presence of a mercaptan cocatalyst and a solid superacid catalyst selected from the group consisting of metal sulfates, sulfated metal oxide, sulfated metal oxyhydroxides, sulfated metal oxysilicates, superacid metal oxides, and mixtures thereof.
JP Patent 62/230741 discloses a purification process for the production of high purity BHPF. The excess phenol present in the reaction media is removed and the crude product is dissolved in a solvent (diethyl ether, acetone, ethanol, propanol, dioxane or acetic acid) able to form an insoluble adduct with BHPF. This adduct is then separated (purity higher than 99%) and recrystallized from the above solvents or aromatic hydrocarbons to obtain further purified BHPF (purity higher than 99.6%).
JP Patent 04/041450 discloses a process for the synthesis of BHPF (or alkyl derivatives) by reacting phenol and fluorenone in presence of metal chloride and HCl or mercaptopropionic acid and HCl. An aliphatic alcohol is added to the reaction mixture to prepare a uniform solution. The BHPF is then precipitated adding water.
JP Patent 04/041451 discloses a process for the purification of colored bisphenols (for example, BHPF and its alkyl substituted derivatives). The crude product is dissolved in aliphatic ketone(s) and after its precipitation is recrystallizated with a mixed solvent of a lower aliphatic alcohol(s) (e.g., methanol, ethanol, n-propanol and isopropanol) and aromatic hydrocarbon(s) (e.g., benzene, toluene and xylene). The method allows colored bisphenols to be purified efficiently, providing colorless products.
JP Patent 63/021836 discloses a purification process for the BHPF where the crude product is first dissolved at room temperature in acetates and then added of a hydrocarbon-based solvent (e.g., hexane) to separate the crystal. The operation can be repeated, as necessary, and the product is finally dried at 100-150xc2x0 C.
JP Patent 08/217713 discloses the use of hydrocarbon based solvents (without hydroxy functions and with a boiling point higher than phenol) as solvent media for the synthesis of BHPF. The unreacted phenol is removed by distillation. The distillation residue is then dissolved in an OH-free organic solvent, heated and cooled to precipitate BHPF.
JP Patent 09/124530 discloses a process for the synthesis of 9-fluorenone and its condensation with phenol in an inert solvent (aromatic hydrocarbon) in presence of acids and a mercaptocarboxylic acid. The BHPF obtained is suitable for the preparation of polyesters, polycarbonates or epoxy resins.
U.S. Pat. Nos. 4,618,699, 4,810,771, 4,904,755 describe a metod for the preparation of polyesters derived from BHPF and aromatic acids. No specific mention is made about the preparation and purification method of BHPF.
The prior art made clear that the purity of the BHPF is an essential condition for obtaining polyesters having superior properties. However, the purification processes described in literature are not able to give an xe2x80x9chigh purity BHPFxe2x80x9d suitable for the use in large scale polycondensation reactions aimed to get polyesters for optical applications. In spite of the extensive prior art cited above, there is still the need of an improved technique for obtaining a extremely pure BHPF for preparation of polyester having superior optical and mechanical properties.
A 9,9-bis (4-hydroxyphenyl) fluorene compound showing a melting curve maximum of at least 226.00xc2x0 C. and a melting curve width at 5% equal to or lower than 1.30xc2x0 C.
A synthesis method for the preparation of 9,9-bis (4-hydroxyphenyl) fluorene compounds comprising the steps of (a) reacting in an organic solvent a phenol compound with a 9-fluorenone in the presence of an acidic condensing agent, (b) separating the crude 9,9-bis (4-hydroxyphenyl) fluorene, and (c) purifying the crude 9,9-bis (4-hydroxyphenyl) fluorene, characterized in that the purifying method comprises a first purification step employing acetonitrile solvent and a second purification step employing a solvent selected from the group consisting of aliphatic alcools, a mixture of aromatic hydrocarbons and aliphatic alcohols and a mixture of aromatic hydrocarbons and nitrites.
A purification process for the preparation of 9,9-bis (4-hydroxyphenyl) fluorene compounds comprising a first purification step employing acetonitrile and a second purification step employing a solvent selected from the group consisting of aliphatic alcools, a mixture of aromatic hydrocarbons and aliphatic alcohols and a mixture of aromatic hydrocarbons and nitrites.